[PATCH AUTOSEL 6.14 377/642] netdevsim: call napi_schedule from a timer context

Sasha Levin
2025-05-05T22:29:12Z

From: Breno Leitao <leitao@debian.org>

[ Upstream commit bf3624cf1c3708284c53ed99a1c43f2e104dc2dd ]

The netdevsim driver was experiencing NOHZ tick-stop errors during packet
transmission due to pending softirq work when calling napi_schedule().
This issue was observed when running the netconsole selftest, which
triggered the following error message:

NOHZ tick-stop error: local softirq work is pending, handler #08!!!

To fix this issue, introduce a timer that schedules napi_schedule()
from a timer context instead of calling it directly from the TX path.

Create an hrtimer for each queue and kick it from the TX path,
which then schedules napi_schedule() from the timer context.

Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250219-netdevsim-v3-1-811e2b8abc4c@debian.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/net/netdevsim/netdev.c | 21 ++++++++++++++++++++-
drivers/net/netdevsim/netdevsim.h | 1 +
2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
index 42f247cbdceec..e4c0d77849b82 100644
--- a/drivers/net/netdevsim/netdev.c
+++ b/drivers/net/netdevsim/netdev.c
@@ -87,7 +87,8 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev)
if (unlikely(nsim_forward_skb(peer_dev, skb, rq) == NET_RX_DROP))
goto out_drop_cnt;

- napi_schedule(&rq->napi);
+ if (!hrtimer_active(&rq->napi_timer))
+ hrtimer_start(&rq->napi_timer, us_to_ktime(5), HRTIMER_MODE_REL);

rcu_read_unlock();
u64_stats_update_begin(&ns->syncp);
@@ -426,6 +427,22 @@ static int nsim_init_napi(struct netdevsim *ns)
return err;
}

+static enum hrtimer_restart nsim_napi_schedule(struct hrtimer *timer)
+{
+ struct nsim_rq *rq;
+
+ rq = container_of(timer, struct nsim_rq, napi_timer);
+ napi_schedule(&rq->napi);
+
+ return HRTIMER_NORESTART;
+}
+
+static void nsim_rq_timer_init(struct nsim_rq *rq)
+{
+ hrtimer_init(&rq->napi_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ rq->napi_timer.function = nsim_napi_schedule;
+}
+
static void nsim_enable_napi(struct netdevsim *ns)
{
struct net_device *dev = ns->netdev;
@@ -615,11 +632,13 @@ static struct nsim_rq *nsim_queue_alloc(void)
return NULL;

skb_queue_head_init(&rq->skb_queue);
+ nsim_rq_timer_init(rq);
return rq;
}

static void nsim_queue_free(struct nsim_rq *rq)
{
+ hrtimer_cancel(&rq->napi_timer);
skb_queue_purge_reason(&rq->skb_queue, SKB_DROP_REASON_QUEUE_PURGE);
kfree(rq);
}
diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
index 96d54c08043d3..e757f85ed8617 100644
--- a/drivers/net/netdevsim/netdevsim.h
+++ b/drivers/net/netdevsim/netdevsim.h
@@ -97,6 +97,7 @@ struct nsim_rq {
struct napi_struct napi;
struct sk_buff_head skb_queue;
struct page_pool *page_pool;
+ struct hrtimer napi_timer;
};

struct netdevsim {
--
2.39.5